Studies will continue on the biochemical development of surface activity of lung of the developing fetus, primarily in primates, including man. Investigations will continue of the enzymatic synthesis of the principal surface active phospholipids, especially under abnormal physiological conditions (hypoxia, acidosis, hypercarbia). Using the amniotic fluid phospholipid lecithin/sphingomyelin (L/S) ratios as the marker of fetal lung maturity, investigations will continue about the mechanisms whereby maternal, fetal and placental conditions influence maturity of fetal lung. Growth of fetuses in utero in abnormal pregnancies will be followed and evaluated. The regulatory mechanisms involved will be studied, including the developmental analysis of steroid binding sites-lung in normal primate pregnancy and in pregnancies stressed experimentally.